The present invention relates to a method of controlling the transmitting power in a mobile radio system and to a corresponding mobile radio system.
Controlling the transmitting power represents an important feature in mobile radio systems in order to prevent possible interference between individual connections. Preventing interference between connections improves the capacity and quality of the connections and allows the mean transmitting power to be reduced. Thus, the transmission power may be ideally adapted to the transmission requirements, and losses through the transmission channels may be at least partially compensated for.
For the purpose of controlling the transmitting power in a mobile radio system, the signal transmitted by a transmitter is evaluated at the receiver. Power control information is generated based on the power of the received signal and is transmitted back to the transmitter. The transmitter may then adjust the transmitting power as necessary in accordance with the received power control information. The received level and/or the received quality of the transmitted signal can be measured by the receiver and values associated with the received level and/or quality may be transmitted to the transmitter. The transmitter correspondingly corrects the transmitting power in dependence on the received values. This approach is used, for example, in Global System for Mobile Communications (GMB) mobile radio systems. Alternatively, the receiver itself can be adapted to generate nominal values or adjustment commands for adjusting the transmitting power in dependence on the measured level of the received transmit signal. The receiver may then transmit these nominal values or adjustment commands to the transmitter which then adjusts the transmitting power accordingly. This approach is used, for example, in Code Division Multiple Access (CDMA) mobile radio systems and, in particular, is provided in accordance with the current state of Universal Mobile Telecommunication System (UMTS) standardization for UMTS mobile radio systems which are to be operated in accordance with a Wideband Code Division Multiple Access (WCDMA) method. In each approach, the power of the transmitter is always controlled in a manner that takes into consideration the current properties of the transmission channel. In each case, the power needed for satisfactory transmission arrives at the receiver as accurately as possible in spite of fading effects.
However, employing this method, the transmitter can only react to the measurements of the receiver. The inherent delay in waiting for the power information feedback signal from the receiver leads to a degradation of the transmission characteristic of the mobile radio system. This is especially true at higher speeds of the receiver.
One proposal for solving this problem for CDMA mobile radio systems has been to reduce the response time or delay in the power control signal to as short a time as possible. This can be achieved by employing a high frequency a power control signal, having a frequency that is as high as possible within the mobile radio system, and clever interleaving of the timeslots of the uplink and downlink connections. In furtherance of this proposed solution, it has been proposed to shift the frame structure of the uplink connection (the connection from the mobile station to the base station) by 250 μs with respect to the frame structure of the downlink connection (the connection from the base station to the mobile station) in order to provide for transmission of the transmitting power control information signal with a time delay of only one timeslot if the symbol transmission rate of the downlink connection is higher than 16 ksps. This proposal is described, for example, in ARIB, Volume 3, Specification of Air Interface for 3G Mobile System, Version 0.5, Section 3.2.2.1.
However, the procedure described above places a premium on the accurate measurement of the channel impulse response of the corresponding transmission channel. This is essential for assessing the behavior and state of the transmission channel since signal distortion can occur due to certain operating conditions. Such signal distortion renders information transmission impossible in the most extreme cases. Therefore, in mobile radio systems the current channel impulse response is measured in the receiver so that if signal distortion is found, the distortion may be subsequently corrected if necessary, using corresponding equalizers.